docs: def _get_site_dummy_variables(self, vs30):
          """
          Returns the Eurocode 8 site class dummy variable
          """
          s_b = np.zeros_like(vs30)
          s_c = np.zeros_like(vs30)
          s_d = np.zeros_like(vs30)
          s_b[np.logical_and(vs30 >= 360., vs30 < 800.)] = 1.0
          s_c[np.logical_and(vs30 >= 180., vs30 < 360.)] = 1.0
          s_d[vs30 < 180] = 1.0
          return s_b, s_c, s_d